Xerographic developer



Dec. 20, 1960 R. w. GUNDLACH XEROGRAPHIC DEVELOPER Filed May 2, 1958 mm mm mm mm Q kw u \w INVENTOR. Robert W. Gundlach ihg g Q QQ United States aten XEROGRAPHIC DEVELOPER Robert W. Gundlach, Spencerport, N.Y., assignor to Haloid Xerox Inn, Rochester, N.Y., a corporation of New York Filed May 2, 1958, Ser. No. 732,644

17 Claims. (Cl. 252-621) This invention relates ot image development of electro static charge patterns.

In order to simplify understanding of this invention it will be exemplified with the art of xerography wherein an electrostatic latent image is formed as through direct charge deposition or exposure of a photosensitive member to a light pattern or the like on an insulating layer 'toner, across the image bearing surface for selective deposition of the toner on the surface in accordance with the charge pattern. Suitable developer mixtures and a full disclosure of their method of use are presented in Us. Patents 2,618,551, 2,618,552, issued on November 18, 1952, and in US. Patent 2,638,416, issued May 12, 1953.

Although the cascade system of image development is the accepted commercial technique to visualize an electrostatic latent image, it inherently does not fully develop large solid areas and frequently there results in the developed image what is generally referred to as the halo effect. Image development with the halo effect and lacking in solid area coverage is today understood to be due to the fact that particle deposition takes place in accordance with electrostatic lines of force rather than as directly controlled by the charge pattern being developed. Considering, for a moment, a large area of charge and realizing that lines of force do not cross and follow the direction of greatest potential gradient to an opposite pole, it can be realized that the charges on the outer edges are terminals for lines of force which extend outward from the surface of the plate and possibly to the next adjacent uncharged area on the surface of the plate. These lines of force near edges of the large areas of charge when developed with a proper developer material can result in particle deposition on the charges of the charge terminal end of the lines of force, thus properly reflecting the pattern. However, at the central zone of the large area of charge the lines of force tend to extend inward through the image bearing member and since development is development of the lines of force, little or no development takes place. One technique of combatting this difficulty is to employ a development electrode or a closely spaced equipotential surface which causes the lines of force to extend outward from the image bearing surface toward the equipotential surface thus causing particles to deposit accurately as a reflection of the original image. The electrode, however, in order to be effective must be close and frequently as, for example, in automatic xerographic machines including cascade developing systems, the narrowness of the gap cannot be maintained "ice without sacrifice in such areas as speed in output or damage to the image bearing surface or member.

Now, in accordance with the present invention, there is disclosed new improved concepts of image development of electrostatic charge patterns. These concepts when employed improve the developed image by fully developing large areas of charge and by avoiding the halo effect. Further, these new concepts when applied in machines do not place limitations, as did known developers and developing systems, on other operational steps. As a further matter and in accordance with this invention a new and improved developer material is disclosed.

Accordingly, it is an object of this invention to define novel methods of image development to visualize electrostatic image patterns.

It is a further object of this invention to improve image development in "the art of xerography.

It is a still further object of this invention to improve developer materials of the cascade variety.

It is yet a further object of this invention to define new xerographic developer materials.

Additional objects and advantages of the present invention will be more readily apparent in view of the following disclosure and description especially when read in conjunction with the accompanying drawing.

In the drawing:

Fig. 1 illustrates cascade development in accordance with the present invention; and

Fig. 2 is an enlarged detail illustration of a section within 2--2 of Fig. 1.

Referring now to Fig. 1, there is illustrated a xerographic plate 11 comprising a photoconductive insulating layer 12 overlying a conductive backing member 13. On the surface of the photoconductive insulating layer 12 is a charge pattern 15 comprising areas of charge and areas of no charge or areas of varying charge. In this figure the charge is illustrated as positive, but as is known in the art, the charge may be negative or even positive and negative. Cascading across the surface of plate 11 is a developer mix of developer 16 which deposits toner particles across the image bearing surface 12 in accordance with the image pattern. Developer 16 and its composition will be more thoroughly discussed hereinafter.

Although there is illustrated in this figure a xerographic plate 12 it is to be realized and understood that there is no intention to be limited to a particular surface bearing the image pattern. The developer and developing systems of this invention are, it is noted, most beneficial when the image surface overlies a conductive member. This is because this invention overcomes the effects of the conductive member. However, comparable quality is obtained whether developing a backed or unbacked image bearing layer and accordingly, any insulating layer is intended to be included herein and xerograpln'c plate 11 is included herein only for illustrative purposes.

In order to more fully understand development in accordance with this invention reference is now had to Fig. 2. Although the illustration of this figure is drawn somewhat to scale to attempt to represent the relationship of particle sizes, the representation is primarily for illustrative purposes and accordingly is somewhat diagrammatic in nature. It is further to be realized that in this figure there is captured for purposes of discussion the cascading particles during an instant of their movement across the image bearing surface. Thus, there is illustrated developer mix 16 comprising carrier particles 17 (only some of which are numbered), toner particles 18 (again only some of which are numbered and filaments 20 (again only some of which are numbered) cascading across plate 11 comprising photoconductive insulating layer 12 overlying backing member 13. As in accordance with the description in Fig. 1 there exists acharge pattern 15 on the surface of image bearing layer 12.

In comparison to prior art techniques of image development there has been added to developer mix 16 filaments 20. Carrier 17, as is fully defined in US. Patent 2,618,551 comprises generally a granular carrier material which is of sufficient specific gravity such as glass, sand or steel beads to insure against adherence of the granular carrier material to the image bearing surface as the carrier cascades across the surface being developed. The granular carrier should also have a desired triboelectric relationship to the toner material and if it is not inherent in the carrier material it may be coated or encased in a suitable covering to impart thereto these necessary properties. Generally the particle size of the carrier material should be in the range of from 20 to 200 mesh and preferably between the range of 30 to 100 mesh.

Toner 18 may comprise any of the known toners defined, for example, in the aforementioned US. patents and may consist, for example, of particles of pigmenting or coloring material encased in or surrounded by an insulating material which acquires by contact with the granular carrier material an electrostatic charge having a polarity opposite to that acquired by the granular material. The coloring material as well as the toner material is fully described in U.S. Patent 2,638,416 and generally should be no larger than 20 microns and preferably is within the range of from 5 to microns average particle size.

The coloring material may be carbon or other suitable pigments and the insulating material may be a rosinmodified phenol-formaldehyde resin, such as known commercially as Amberol F-7l, manufactured by Rohm & Haas Company, The Resinous Products Division, Washington Square, Philadelphia 5, Pennsylvania, or asphaltum, or other suitable material.

The pigmented electroscopic powder is prepared by first micronizing the resin material, such as Amberol F-7l, after which it is mixed with approximately 5% by weight of carbon black or other pigmenting material and the mixture ball-milled for about four hours in a ceramic jar with stone pellets. The mixture is then heated to a temperature of about 300 F. or to flowing viscosity and mixed for five minutes in order to encase the pigmenting particles with the Amberol F-7l. The mass is then permitted to cool, after which it is broken into small chunks and again micronized.

The pigmented electroscopic powder is then in condition for mixing with a granular carrier such as polymerized methyl methacrylate, having a melting point of approximately 257 F., known commercially as Lucite and manufactured by E. I. Du Pont de Nemours & Company, Wilmington, Delaware, or other material either conducting or insulating, provided the particles of granular material when brought in close contact with the electroscopic powder particles acquire a charge having an opposite polarity to that of the electroscopic powder particles, such that the electroscopic powder particles adhere to and surround the granular carrier particles. The granular carrier material is selected so that the particles acquire a charge having the same polarity as that of the photoconductive insulating layer of the plate on which the electrostatic image is produced, and an electrical attraction for the electroscopic powder particles considerably less than that of the charged areas of the plate and somewhat greater than the discharged areas of the plate.

Generally the mixture of toner and carrier comprises 1 part toner mixed with from 20 to 200 parts carrier and preferably the mixture comprises 1 part toner to 50 to 120 parts carrier.

Filaments 20 are conductive strands and may comprise, for example, conductive wires, conductive strings or the like. Their length generally should be greater than 956 inch and the upper limit on length is generally about inch, but as will appear more clearly in the following discussion, greater lengths are also possible. The preferred length for filaments 20 is between /8 and /2 inch, and for the typical range of material generally reproduced an average length of about A inch is preferred. The diameter of filaments 20 may range from 1 to 20 mils and is preferably between 3 and 10 mils. Triboelectrically, filaments 20 should be opposed in polarity to the toner while like in polarity to the carrier or should charge the toner to the same polarity as the toner charge when the toner 18 is brought into physical contact with carrier 17. Filament 20 should also be substantially neutral triboelectrically in respect to carrier 17. Typically, filaments 20 may comprise Nichrome, steel, aluminum, copper, brass and particularly yellow brass, nickel, and the like. The material chosen preferably should be a stable material which, for example, resists oxidation which might act to change its triboelectric relationship to toner 18 and carrier 17. A particularly effective and the preferred filament material for a positive developer wherein the carrier material comprises a resin-coated bead and the toner material comprises, for example, the Amberol F-7l mixture described previously and the toner material becomes charged negatively in relation to the carrier material on mixing with the carrier material is Nichrome chopped strands. A reversal mixture wherein the toner is charged positively in respect to the carrier comprises nickel-coated copper or copper strands which have been exposed to sulphur fumes at a high temperature. When employing both carrier particles 17 and toner particles 18, filament particles 20 may be mixed with the carrier toner mixture in a ratio of from parts developer (carrier and toner) to 5 to parts filament and preferably the mixture may comprise 100 parts developer to 20 to 1.00 parts filaments. The preferred developer mixture including filaments as illustrated in Fig. 2 comprises 49% carrier 17, 49% filament 20 and 2% toner 18.

It is to be realized that the filament material being discussed may vary in length and diameter and that the amount of filament material mixed with a developer mix is dependent to some extent on these variables. For example, if filament 20 comprises a long length such as /1 inch then a tendency exists for filaments 26 to cluster and there follows a flowing of the filaments 20 across image bearing surface 12 as a clustered group. When this occurs a raking of the image is observed. This clustering and raking problem can be overcome to some extent by using large diameter filaments when employing long lengths in the filament material. A further technique of avoiding the clustering effect is to employ a low percentage of filament 20 to developer mix somewhere, for example, in the range of 2% to 3%. If shorter lengths as, for example inch are used larger percentage ratios of filament to developer may be employed.

The mechanism of operation now believed to effect large, solid area coverage as well as to avoid the halo effect is believed somewhat apparent when considering Fig. 2. For example, filament 20 also designated 21, it is to be observed, extends across a charged area as well as an uncharged area of image bearing surface 12. Since filament 21 is conductive, it, like any other conductor, has a supply of free electrons and while over both a charged and an uncharged area there is a flow within filament 21 controlled by the surrounding electric fields. There thus results polarization of charge within this filament so that negative charge appears over the positively charged areas of plate 11 and positive charge appears over the uncharged areas of plate 11. This member although polarized remains an equipotential member and thus presents a close- 1y spaced equipotential surface to the image bearing surface 12. Since the negative charged area of filament 21 is positioned over the positive charged area of image bearing surface 12 strong electrostatic lines of force exist between the positive charges and filament 21 and thus lines of force extend directly outward from the surface of plate 11. There follows particle deposition in accordance with linesof force as disclosed previously and there results particle deposition in accordance with the charge pattern. It is noted that areas of filament 21 over uncharged areas of image bearing surface 12 are positive with respect to the image bearing surface and thus there follows a tendency to avoid particle deposition on the image bearing surface in these areas. Acc0rdingly, filament 21 when positioned as illustrated in Fig. 2 acts first to cause particle deposition in accordance with the charge on the surface being developed as well as to prevent deposition in areas of background thus producing background-free high quality copy. Considering now filament 20, also designated 22, it is seen that this filament is positioned over an uncharged area. Being over an uncharged area it is in a neutral condition and will tend to have no real effect on whether particles deposit or do not deposit on the surface of image bearing layer 12. In fact it will act as any carrier particle. Looking now to filament 20, also designated 23, it is seen that this particle is in physical contact with filament 20, also designated 25, which is in contact with filament 20, also designated 26, which is in contact with filment 20, also designated 27, which is in contact with filament 20, also designated 21. Since these filaments are conductive and are in contact, filament 23 will assume a slightly positive relationship in respect in respect to the uncharged area of photoconductive insulating layer 12 over which it is now positioned. This will aid also in preventing background deposition.

It is to be realized that Fig. 2 illustrates a brief moment in the flow of the cascading developer 16 across plate 11 and that a moment later this contact relationship between various filament particles is likely to be broken and a moment later it may be made anew with other particles, etc. Accordingly, there is a continuing change of filament reltaionship to the surface being developed, but as this change takes place and as the developer mixer moves across the surface of the plate, developrnent electrode effects through the flowing filaments are extended to all areas of the plate to a substantially average level and result in a uniform high quality image developed in accordance with the charge pattern. It is also to be noted that control of the developed image may be exercised through control of the developer mixture. Thus, and for example, if it is desired to develop large charged areas it is generally preferred to use longer filaments whereas with the average mixture of broad areas of charge and narrow areas of charge it is generally preferred to use an intermediate length in the filament material and with relatively small broad areas of charge it. is generally preferred to use the shorter length filaments. It is noted that the length of filament chosen is selected because of its bridging capabilities. Thus, with the larger areas of charge it is preferred to have a long filament in order that probability of bridging from the broad area of charge to the uncharged area is greater thereby effecting particle deposition in the central zone more readily than if shorter filaments are employed. This may also be accomplished, however, if a larger percentage of the smaller particles are incorporated into the developer mix.

As is apparent in the illustration in Fig. 2, toner particles 18 also adhere in a releasable fashion to filament 20. This is because of the triboelectric relationship between the toner particle 18 and the filament 20, and adherence between toner particle 18 and filament 20 in no way detracts from the quality of the image developed.

In fact, developer mixtures excluding carrier 17 have been tried and have been very successful in developing images. It is noted in this respect that filament 20 is after all of the same triboelectric relationship to the toner as the carrier material and accordingly can act as the carrier material. A problem, however, which has been present to date employing filament 20 as both filament 20 and carrier 17 is the tendency for the developer mixture to rake the surface being developed. Thus, the developed image occasionally includes a streaked pattern as if raked whenthe carrier is omitted; whereas, with a developer mixture employing a carrier material 17 this pattern is avoided. It is presently believed that the carrier material is beneficial in providing the wheels to cause the entire developer mixture 16 to roll across the surface being developed without dragging or raking as it apparently occasionally does without carrier 17. Accordingly, it is generally preferred that developer mixtures according to this invention also include carrier 17, and carrier 17 may be composed of the same material as filament 20. When carrier material 17 is not present in the developer mixture, then the developer mixture may comprise 1 part toner 18, to 20-200 parts filament and preferably 1 part toner to 50-120 parts filament.

In summary, filaments 20 added to xerographic cascade developers in accordance with this invention should comprise a good electrical conductor having a substantially neutral triboelectric relationship to the carrier and the same triboelectric relationship to the toner as the carrier has to the toner and. should be in strip, chopped wire or filament-like form whereby conductive bridging of an area over the surface being developed can readily take place.

What is claimed is:

1. A xerographic developer for electrostatic latent images comprising, in mixture, a first component comprising granular carrier particles having a size range of from 20 to 200 mesh, a second component comprising filamentary electrically conductive particles having a length in the range of from about ,6 inch to about /1 inch and having diameters in the range of about from 1 to 20 mils, and a third component comprising pigmented toner powder particles no larger than about 20 microns, each of said first and said second components being triboelectrically different from said third component and each having a triboelectric relationship of like polarity with respect to said third component and said second component having a substantially neutral triboelectric relationship with respect to said first component, a developer mixture comprising one part of said third componeat to 20 to 200 parts of said first component and the first and third component mixture comprising about parts to about 5 to 150 parts of said second component.

2. A xerographic developer for electrostatic latent images comprising, in mixture, a first component comprising granular carrier particles in' the size range of about from 30 to 100 mesh, a second component comprising filamentary electrically conductive particles having lengths in the range of from about A; to /zinch and having diameters in the range of from about 3 to 10 mils, and a third component comprising: pigmented toner powder particles in the range of about. 5 to 10 microns in size, each of said first and said second components being triboelectrically different from said third component and each having a triboelectric relationship of like polarity with respect to said third component and said second component having a substantially neutral triboelectric relationship with respect to said first component, one part of said third component being mixed with 50 to parts of said first component and 100 parts of the mixture of said first component and said third component being mixed with 20 to 100 parts of said second component.

3. A developer in accordance with claim 2 in which the carrier comprise about 49% by weight of the mixture, the filamentary particles comprise about 49% by weight of the mixture, and the toner material comprises about 2% by weight of the mixture.

4. The developer of claim 2 in which said second component comprises filamentary electrically conductive particles having a length of about A inch.

-5. The developer of claim 2 in which said second component comprises Nichrome.

6. The developer of claim 2 in which said second component comprises nickel-coated copper.

7. The developer of claim 2 in which said second component comprises copper strands which have been exposed to sulphur fumes at a high temperature.

8. A developer for electrostatic latent images comprising, in mixture, a first component comprising filamentary electrically conductive particles having a length in the range of from about ,6 to inch and having diameters in the range of from about 1 to 20 mils, and a second component comprising pigmented toner powder particles no larger than about 20 microns, said first and said secnd components being admixed one part of said second component to about 20 to 200 parts of said first component, said first and said second components being triboelectrically diiferent from each other to cause said second component to electrostatically adhere to said first component when said first and said second components are admixed and said triboelectric relationship being of an intensity to allow said second component to be released to an electrostatic charge pattern when said mixture of said first and said second component are cascaded across an electrostatic image bearing surface.

9. The developer of claim 8 in which said first component comprises Nichrome.

10. The developer of claim 8 in which said first component comprises yellow brass.

11. The developer of claim 8 in which said first component comprises nickel-coated copper.

12. The developer of claim 8 "n which said first component comprises copper strands which have been exposed to sulphur fumes at a high temperature.

13. A developer for electrostatic latent images comprising, in mixture, a first component comprising filamentary electrically conductive particles having an average length of about A inch and having diameters in the range of from about 3 to 10 mils, and a second component comprising pigmented toner powder particles in the size range of from about 5 to microns, said first and said second components being admixed one part of said second component to 50 to 120 parts of said first component, said first and said second components being triboelectrically different from each other to cause said second component to adhere to said first component when said first and said second components are admixed and said triboelectric relationship being of an intensity to allow said second component to be released to an electrostatic charge pattern when said mixture of said first and said second component are cascaded across an electrostatic image bearing surface.

14. A xerographic developer for electrostatic images comprising, in mixture, a first component comprising granular carrier particles having a size range of from about 30 to about 100 mesh, a second component comprising filamentary electrically conductive particles having a length of about inch to about /2 inch and having a diameter in the range of from about 3 to about 10 mils, and a third component comprising pigmented toner particles in the range between about 5 to about 10 microns, said components being admixed one part of said third component to 50 to parts of said first component and the third and first component mixture being admixed with said second component in a ratio of 100 parts of the mixture of the third and first components to 20 to 100 parts of said second component.

15. The developer of claim 14 in which said second component comprises filamentary electrically conductive particles having a length of about inch.

16. A developer for electrostatic latent images comprising, in mixture, a first component comprising granular carrier particles having a size range of from 20 to 200 mesh, a second component comprising filamentary particles of yellow brass having a length in the range of about inch to about inch and having a diameter in the range of about 1 to 20 mils, and a third component comprising pigmented toner particles no larger than about 20 microns, each of said first and said second components being triboelectrically different from said third component and each having a triboelectric relation of like polarity with respect to said third component and said second component having a substantially neutral triboelectric relationship with respect to said first component, said developer comprising a toner carrier mixture in mixture with yellow brass, said toner carrier mixture comprising one part toner to 20 to 200 parts carrier, and said developer comprising about 100 parts of said toner carrier mixture in mixture with about 5 to parts filamentary particles of yellow brass.

17. A xerographic developer for electrostatic latent images comprising, in mixture, a first component comprising granular carrier particles having a size range of from 20 to 200 mesh, a second component comprising filamentary electrically conductive particles having a length of from about inch to about inch and having a diameter in the range from about 1 to 20 mils, and a third component comprising pigmented toner powder particles no larger than about 20 microns, said mixture comprising one part toner to 20 to 200 parts carrier and the toner carrier mixture comprising about 100 parts to about 5 to 150 parts filamentary particles.

References Cited in the file of this patent s. 112...), r' a 

1. A XEROGRAPHIC DEVELOPER FOR ELECTROSTATIC LATENT IMAGES COMPRISING, IN MIXTURE, A FIRST COMPONENT COMPRISING GRANULAR CARRIER PARTICLES HAVING A SIZE RANGE OF FROM 20 TO 200 MESH, A SECOND COMPONENT COMPRISING FILAMENTARY ELECTRICALLY CONDUCTIVE PARTICLES HAVING A LENGTH IN THE RANGE OF FROM ABOUT 1/16 INCH TO ABOUT 3/4 INCH AND HAVING DIAMETERS IN THE RANGE OF ABOUT FROM 1 TO 20 MILS, AND A THIRD COMPONENT COMPRISING PIGMENTED TONER POWDER PARTICLES NO LARGER THAN ABOUT 20 MICRONS, EACH OF EACH AND SAID SECOND COMPONENTS BEING TRIBOELECTRICALLY DIFFERENT FROM SAID THIRD COMPONENT AND EACH HAVING A TRIBOELECTRIC RELATIONSHIP OF LIKE POLARITY WITH RESPECT TO SAID THIRD COMPONENT AND SAID SECOND COMPONENT HAVING A SUBSTANTIALLY MENTRAL TRIBOELECTRIC RELATIONSHIP WITH RESPECT TO SAID FIRST COMPONENT, A DEVELOPER MIXTURE COMPRISING ONE PART OF SAID THIRD COMPONENT TO 20 TO 200 PARTS OF SAID FIRST COMPONENT AND THE FIRST AND THIRD COMPONENT MIXTURE COMPRISING ABOUT 100 PARTS TO ABOUT 5 TO 150 PARTS OF SAID SECOND COMPONENT. 